METALLURGY OP IRON AND STEEL.
contain 16.67 per cent, of Si02 and 50 per cent. CaO, the basic additions must contain ~^=thiee times as much available CaO as there is Si02 in the charge, and the final slag will weigh six times as much.
TABLE XI-B. Elimination of Phosphorus and Carbon During Melting.
Pounds of ore charged with stock, per ton of metal. Numher of heats in group. Composition of metal, per cent. Composition of slag after melting; per cent.
Initial. After melting. Per cent, eliminated. Initial. After melting. Per cent, eliminated.
none, none, none, none. 800 115 140 17 4 9 9 8 6 7 0.20 1.86 0.19 0.19 2.50 0.55 0.55 .046 .594 .023 .072 .744 .274 .402 77 57 88 62 70 50 27 2.00 1.60 1.80 1.80 3.50 2.90 2.90 .71 .60 .27 .78 .59 1.00 1.48 65 60 85 67 83 65 49 19.21 14.90 15.55 19.98 11.96 80.73 84.22 18.68 und. 19.68 12.20 8.61 10.71 10.95
The composition of the cinder differs considerably,, for when good stock is used it may contain over 20 per cent, of silica and still be capable of eliminating the impurities, but when much phosphorus is to be removed, the silica must sometimes be as low as 12 per cent., the proportion of CaO usually varying inversely with the silica. The amount of lime which can be taken up is, limited, for at a certain point the slag becomes viscous, particularly when the scorification of the hearth supplies magnesia. Allowing for 10 per cent, of MnO, 8 per cent. MgO, 18 per cent. FeO, and 4 per cent. A1208, etc., it may be stated that with 12 per cent, of Si02 there will be 48 per cent. CaO, while with 20 per cent, of Si02 there will be 40 per cent. CaO. In the attainment of this ratio between Si02 and OaO the purity of the lime is an important factor, especially when a slag low in silica is needed. Ordinary lime contains a certain percentage of C02, and a certain amount of moisture, so that with the usual proportions of earthy impurities it will average about 80 per cent, of CaO.
SEC. Xlg.—Relative value of limes.—The content of Si02 in the lime depends upon the kind of stone used and the care with which the ash of the fuel is kept separate. When a choice must be made between a cheap and impure lime and a more costly. article low in silica, the value of each may be calculated by finding the excess of